This could happen if:
There are a few checks we would suggest you try. If you open System Configuration (msconfig), you may find that there is no Boot data. It has been reported that the primary reason why this occurs is that when the user tries to dual boot the computer and the installer replaces the default bootloader.
The boot configuration data store could not be opened
Just before we start, know this. In earlier versions of Windows, it was stored in Boot.ini file. On EFI-based operating system, you’ll find the entry in the EFI firmware boot manager, which is located at \EFI\Microsoft\Boot\Bootmgfw.efi. The options you have to resolve the issue are: These steps can be performed by booting your computer into Advanced Recovery Mode. It offers Command Prompt which is available under Advanced Options. Also, before setting BCDEdit options, you might need to disable or suspend BitLocker and Secure Boot on the computer.
1] Set an entry option value in BCD
Open Command Prompt as administrator Execute the following command: The /set option sets an entry point and enables the system to trust a version of Windows which is not trusted by default.
2] Specify the BCD file
In an elevated command prompt execute: It will give you a list of options. Choose to run: Restart your computer, choose your Windows, and immediately press F8. When you choose the legacy option, the Advanced options menu (F8) is available during the computer boot up. Then you can choose into which OS to boot.
3] Rebuild BCD
If it does not work, you may have to rebuild BCD. You can manually rebuild the Boot Configuration Data store by using the Bootrec.exe tool in the Windows Recovery Environment, or you can use this free BCD Editor tool to repair BCD. Hope this helps you fix the issue.
